There is substantial interest in improving the performance characteristics of athletic and walking shoes. Much recent industry interest relates to the manufacture of footwear having energy return characteristics. There is also a substantial interest in the ease of manufacturing such shoes.
Initial efforts directed at providing energy return systems were primarily directed to improving the cushioning and shock absorption with a range of synthetic materials. In particular, microcellular closed cell material and polyurethane systems have long been used in the commercial manufacture of a variety of midsole and wedge components intended to improve the comfort, cushioning and shock absorption of footwear. Other energy return systems have contemplated the use of thermoplastic hollow tubes or shapes encapsulating a fluid or gas that are strategically located in the midsole or elsewhere to provide an energy return mechanism to the shoe. Still other systems contemplate the use of such commercially available materials as HYTREL® and KEVLAR® in various blends, compositions and molded arrangements positioned in the arch and/or medial portion of the shoe providing mechanical cushioning and energy storage.
Netting or grid mesh arrangements have also been used in selected portions of a sole construction for various purposes. An example of one of the earliest of such efforts was in the form of a fine woven wire fabric described in U.S. Pat. No. 812,496, issued Feb. 13, 1906. Mesh used in that construction, however, provided only stiffness and wearing qualities at the bottom of the heel. That patent failed to suggest arranging the mesh under appropriate tension and thus fails to teach or suggest the use of such mesh in an energy return system. A second disclosure of a mesh construction is contained in U.S. Pat. No. 1,650,466 issued Nov. 22, 1927. In that construction, a fabric of mesh is used to retain the shape of a component and does not act as an energy return system such as a spring or the like.
More recently, U.S. Pat. No. 4,297,796, issued Nov. 3, 1981, discloses the use of an open work support or netting of stretch resistant threads secured to the top side of a flexibly deformable sole layer. This netting structure is intended to distribute shock stresses in the heel or ball of the foot. Since that open mesh is three-dimensional, it redistributes deformation of the sole structure under compression and does not function as a spring-like energy return system. Similarly, U.S. Pat. No. 4,608,768, issued Sep. 2, 1986 discloses the use of an open work structure embedded in a resilient member with plugs arranged within the openings of the open work structure. In such an arrangement, different shock absorbing characteristics may be imparted to selected portions of the sole structure. The mesh arrangement, itself, however does not appear to be used as a spring-like energy return system.
Most recently, U.S. Pat. No. 5,070,629, issued Dec. 10, 1991, discloses an energy return system that includes a rigid frame with a set of monofilaments or fibers secured under tension across the frame. The monofilaments or fibers form a spring-like system that stores energy during the compression portions of the gait cycle and releases energy during the push-off phase of the gait cycle. U.S. Pat. No. 5,402,588, issued Apr. 4, 1995, U.S. Pat. No. 5,561,920, issued Oct. 8, 1996, and U.S. Pat. No. 5,595,002, issued Jan. 21, 1997, disclose various improvements to this spring-like energy return system.
As stated above, there is a substantial interest in the ease of manufacturing such shoes. Typically athletic and walking shoes are manufactured by first forming and shaping the upper onto a last. The upper is then secured in this shape by attaching the upper to a stroble board along the bottom of the last. The stroble board is typically a thin fiberboard material. Thereafter, the midsole and outsole are secured, forming the shoe, and the stroble board is typically adhered to a portion of the sole of the shoe.
However, the present invention incorporates an energy return system into a midsole insert that thereby eliminates the need for a stroble board. The midsole insert of the present invention includes a plurality of grid systems which function as an energy return system, and further, the midsole insert may be attached directly to the upper during manufacturing, such that a conventional stroble board is not required.